Semiconductor devices are obtained from processed wafers by various methods. One such method is performed by (a) securing one or more wafers on an adhesively coated layer of material, (b) scribing the appropriate matrix of lines on each wafer, and then (c) breaking the scribed lines by moving a weighted roller over each wafer. In this regard see, for example, U.S. Pat. Nos. 3,040,489 (issued to H. Da Costa on June 26, 1962) and 3,206,088 (issued to A. Meyer et al. on Sept. 14, 1965). Various other methods can then be used to separate the individual devices using plungers, air pressure and the like to expand the adhesively coated layer and spread the broken lines. In this regard see, for example, U.S. Pat. Nos. 3,562,057 (issued to K. W. McAlister et al. on Feb. 9, 1971) and 4,296,542 (issued to A. Gotman on Oct. 27, 1981.)
Another method for obtaining semiconductor devices from a wafer is shown in FIG. 1 by sawing completely through a wafer 10 in orthogonal directions with a saw 11 after the wafer 10 has been mounted on a thin tape 12 or adhesive material within a frame 13 that is held on a saw chuck 14 by vacuum introduced through holes and channels 15. In this regard see, for example, U.S. Pat. Nos. 2,762,954 (issued to M. Liefer on Sept. 11, 1956). There, a semiconductor wafer is securely mounted to a plate with a thin adhesive layer of pitch or the like. A saw then cuts through the wafer and partially into the adhesive layer. The resulting semiconductor devices are then further processed or removed from the plate.
In general, when a tape layer 12 is used to secure the wafer 10, and the sawing operation is finished to form semiconductor devices 16, the vacuum on the saw chuck 14 is switched off, and air is forced through holes and channels 15 in chuck 14 and under the tape 12, as shown in FIGS. 2 and 3, in order to break the seal between an upper surface 17 of chuck 14 and the tape 12. This seal is usually enhanced by surface tension of water used for the cutting operation that becomes trapped between the chuck 14 and the tape 12. Because of such enhanced surface tension, sections of tape 12 release at different times when air pressure is applied as shown in FIG. 2, or do not release at all until pressure is applied to frame 13, either manually or by an automatic handler. This sectional releasing results in rejectable chipping to the edges of the semiconductor devices 16 as the devices 16 are tilted in relation to each other and the top edges clash together as shown in FIG. 2. If it were possible to release all of tape 12 at the same time, tape 12 would become domed and the die prevented from touching each other as shown in FIG. 3.
Attempts have been made to solve this problem by altering the design of the top surface 17 of vacuum chuck 14. Some chucks 14 have a roughened surface so that surface tension effects are not as severe, while others have many fine circular, or other configuration, channels connected to each other so that the air pressure will release all areas at the same time, as shown, for example, in FIGs. 1 or 7 in U.S. Pat. No. 2,443,983 (issued to C. Morrison et al. on June 22, 1948) or FIG. 1 of U.S. Pat. No. 4,506,184 (issued to G. J. Siddall on Mar. 19, 1985). However, these approaches do not consistently solve the problem and the situation becomes even worse as device 16 sizes become larger. When one area of the tape 12 separates from the chuck 14, the air escapes through that section and the remainder of the tape 12 is still held on chuck 14. Roughening the sawing tape 12 to reduce the surface tension also does not provide a solution since, when the wafer 10 is mounted to a roughened tape 12 under the influence of heat and pressure, the roughening tends to be removed from the tape 12. Furthermore, if the roughening of tape 12 is not totally removed, then the wafer 10 is not held as firmly as required. Therefore, the problem still remains to provide a technique for ensuring the concurrent release of the tape 12 from the entire upper surface 17 of the chuck 14.